Filter unit having a circumferential electrostatic shield

ABSTRACT

The unit includes an extended foil capacitance section made up of at least a pair of electrodes convolutely wound in a capacitance relation with dielectric spacing material therebetween. A lead extends through the section in connection to one electrode, and the other electrode volutely extends beyond the one electrode to provide an electrostatic shield for the unit.

United States Patent [56] References Cited UNITED STATES PATENTS1,658,501 2/1928 Valle.......,.,.,,

[72] Inventor Walter F. England Williamstown, Mass.

[2|] Appl .No. 22 Filed 2, ,44l 5/1935 2,260,296 10/194] Christopher etal. 2,526,321 l0/l950 Beverly Primary Examiner-Herman Karl SaalbachAssistant Examiner--Paul L. Gensler Attorneys-Connolly and Hutz, VincentH. Sweeney, James P.

[54] mmn unrr HAVING A CIRCUMFERENTIAL Sullivan and David ELECTROSTATICSHIELD 9 Claims, 5 Drawing Figs.

[52] U.S.Cl.....;...........

connection to one electrode, and the other electrode volutely extendsbeyond the one electrode to provide an electrostatic FILTER UNIT HAVINGA CIRCUMFERENTIAL ELECTROSTATIC SHIELD BACKGROUND OF THE INVENTION Thisinvention relates to filter units and more particularly to an economicalfilter unit which utilizes a metal film as an external shield.

In the prior art, wave filters are generally constructed with anexternal metal housing connected to the ground side of the capacitiveelement for shielding of the enclosed components from external fields.This provides a comparatively costly structure which limits itsapplications.

One object of this invention is to provide an economical filter unit.

Another object of this invention is to provide a filter unit having aneconomical outer shield.

A further object of the invention is to provide a filter unit having theground electrode convolutely extended beyond the other electrodes so asto provide an electrostatic shield.

A still further object of this invention is to provide a filter unithaving a metallized film casing.

SUMMARY OF THE INVENTION A filter unit constructed in accordance withthe invention comprises a capacitive section having at least a pair ofelectrodes convolutely wound in capacitive relation with dielectricspacing material therebetween, each electrode is extended from arespective end of the section, a lead extends through the center of thesection and is in connection to one electrode, and the other electrodeis volutely extended beyond the end of said one electrode so as tothereby provide a shield for said filter unit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in section of afilter unit provided in accordance with the invention;

FIG. 2 is a sectional view of the capacitance section of FIG. 1 takenalong a plane perpendicular to its convolute winding;

FIG. 3 is a view in section of another embodiment of the filter unit;

FIG. 4 is a view in section of an embodiment of the invention whichprovides a T-type filter unit; and

FIG. 5 is a view in section of a qr-type filter unit provided inaccordance with the invention.

DESCRIPTION OF THEPREFERRED EMBODIMENT FIG. 1 shows a filter unit havingan extended-foil capacitance section 12 affixed at one end to a bulkheadterminal member 14. Section 12 is shown in FIGS. 1 and 2 as being aconvolutely wound section having electrodes 16 and I8 wound in extendedfoil fashion with interposed dielectric spacer material 20 and 22.

Section 12 is affixed to terminal 14 by connection of electrode 18 tothe terminal by solder 24 or the like. A feedthrough lead 26 isconnected to electrode 16, by solder 28 or the like at the other end ofsection 12. Lead 26 passes through mandrel hole or bore 30 of section 12and is insulated from terminal 14 by a dielectric plastic material 32such as an epoxy resin or the like which is molded within mounting stud34 of terminal 14.

Shielding of filter unit 10 is provided in this embodiment byconvolutely extending the ground electrode or terminal connectedelectrode, that is, electrode 18 in this case, beyond the electrode 16as depicted in FIG. 2. As shown in this figure, electrode 18 isconvolutely extended to and preferably beyond the end 36 of electrode 16such that electrode 18 provides a circumferential shield encompassingsection 12. Advantageously, dielectric 22 is also convolutely extendedwith electrode 18 to provide an insulative covering around the unit.

The unit is constructed by first winding a section 12 in a conventionalmanner, with however, one foil convolutely extended outside of the otherand preferably beyond the end thereof. The outside foil is thenconnected to the terminal or ground side of the filter unit while theother, inner, electrode is connected to a feed-through lead as shown.

Of course, many different materials may be employed in thisconstruction. For example, section 12 may be constructed from metal foilsuch as zinc or aluminum or the like and dielectric spacer strips ofkraft paper or suitable plastic or the like.

Metallized film-type sections may also be employed. Advantageously, ifthe section is rolled with its metallic deposit on the inner surface ofthe plastic film, an outer insulative covering having an innerconductive shield is inherently provided.

The shielding casing can also be provided by a metallized tape or sleeve40, as shown in FIG. 3, which is in connection to ground electrode I8and provides a shieldlike extension of it. Sleeve 40 is made up of adielectric film 42 such as polyethylene or the like which is coated onits inner surface with conductive material 44 of aluminum or the like.

Casing 40 is constructed so as to allow contact of its inner conductivedeposit 44 to ground electrode 18 of the filter. This is accomplished inthe illustrated embodiment by contact of film 44 to an outer portion ofheader l4. Conductive film 44 is extended throughout the full length ofthe section but spaced from the positive or line side of the filterunit; that is, the metallizing 44 is terminated at the corner 46 and isspaced from the positive electrode 16 and its interconnecting solder 28.This provides an effective Faraday shield on the unit 10 whichterminates or grounds external electrostatic fields. Consequently, anystray fields must feed into the line on its positive side.

FIG. 4 illustrates a T-type filter which is constructed in a mannersimilar to that described above, with however, the addition of inductors50 and 52 spaced at either end of the section 12. Inductive element 50and 52 are connected in series with lead 26. Inductor 50 is disposed, inthis case, within the plastic seal 32 of bulked mounting terminal 14while inductor 52 is disposed in additional plastic material 54 whichcovers the line end ofthe section 12.

An insulative washer 56 is disposed between element 50 and the adjacentend of section I2 and a pair of similar washers 58 and 60 are providedat the other end of the section to insure insulation of inductor 52. Itshould be noted that washer 60, which is mounted at the extreme end ofthe unit provides support for the film 42 which in this case is extendedaround inductor 52 at the positive end of the unit.

As in the previously described embodiments, the shielding deposit 44 isstopped just prior to the positive end of section 12, so as to preventany possibility of contacting the positive electrode or inductor 52. Theconductive shield 44 may, of course, be extended alongside inductor 52if steps are taken to provide adequate insulation between the shield andthe line elements.

Advantageously, an L-type unit can be provided by eliminating one or theother inductor elements. Preferably, inductor 50 is retained since thisprovides a more compact unit in which the inductor is convenientlydisposed within the header 14. It should be understood, of course, thatin structures where room for the inductive element 50 is not permittedwithin the header it may be advantageous to provide the L-type unit withan inductive element disposed at the positive end of the filter.

The mandrel hole 30 may also be utilized to store the inductor, forexample, ferrite beads or a ferrite slug inductor may be mounted on lead26 and disposed within mandrel hole 30 of section 12 to provide L- andT-type filter units.

A rr-type filter may also be constructed in accordance with theinvention as shown in FIG. 5 wherein a pair of concentric capacitancesections 64, 66 are interconnected with an inductive element 68.Inductor 68, which may be a coil or the like is mounted at the positiveend of the filter structure in series connection between the positivefoils of section 64 and 6.6.

Hence, coil 68 is connected at one end to lead 26, which is connected bysolder 70 to the positive electrode (not shown) of the inner capacitancesection 64, while the other end of inductor 68 is connected to thepositive electrode (not shown) of capacitance section 66 by a ring 72 ofsolder or the like, which is concentric to solder 70. A line terminal 74is also provided in connection to the positive foil of capacitor 66 bysolder 72. The negative or ground electrode of each section is connectedto terminal 14 by solder as shown at 76, and the unit is completed byenclosing section 66 and coil 68 within metallized film 40.

in this construction metallic deposit 44 is longitudinally extendedbeyond the end of section 66 and alongside inductor 68 so as to alsoprovide an electrostatic shield for this element. It should beunderstood, of course, that shield 44 may also be brought around the endof the unit as long as it is adequately insulated from both theinductive element and the positive electrodes.

Many different embodiments are possible, of course. For example, theinductive elements may be inductive coils having molybdenum cores or thelike; or may be other inductive components. In addition, morecomplicated filters may be constructed in the above manner for example,by splitting its capacitive windings into more portions and utilizingadditional inductive elements.

In the ar-type unit of FIG. 5, as well as in any of the otherembodiments, the outer shield may be conveniently provided byconvolutely extending the ground electrode of the outermost section(section 66 in this case) beyond its negative electrode.

The metallized film may be employed in any embodiment as a shield ifdesired, and contact to the ground side of the unit may be by means ofthe ground terminal or by direct contact to the ground electrode at thecircumference of the capacitance section.

Where a metallized sleeve or the like is utilized, the ground electrodeneed not convolutely extend beyond the negative electrode since thesleeve serves as the electrostatic shield, however, the negativeelectrode must in any case be circumferentially insulated, as forexample by convolutely extending one of the dielectric spacers of thesection outside of this electrode and at least to its end.

As indicated, sleeve 40 may be a tape wound around and affixed to theunit, for example by an adhesive between its overlapping portions, ormay be a heat shrinkable tubing which is thermally shrunk around section12 and header 14.

Thus many different embodiments are possible without departing from thespirit and scope of the invention, and it should be understood that theinvention is not to be limited except as in the appended claims.

What I claim is:

l. A filter unit comprising a capacitive section having at least a pairof electrodes separated by dielectric material and convolutely wound incapacitive relation, one of said electrodes extended from one end ofsaid section and interconnected thereat, the other of said electrodesextended from the other end of said section and interconnected thereat;a lead extended through the center of said section, said lead inconnection to said one electrode at said one end and insulated from saidother electrode, and said other electrode volutely extended by ametallized film circumferentially shrunk around said section with itsmetallic deposit in connection to said other electrode at said other endfor providing a circum ferential electrostatic shield ofsaid unit.

2. The filter unit of claim 1 including an inductive element disposed atone end of said section in connection to said one electrode.

3. The filter unit of claim 1 wherein said metallized film is a sleeveof shrinkable material, said sleeve having said metallic deposit on theinner surface thereof, and said sleeve shrunk fit around said section toprovide said connection between said deposit and said other electrode.

. The filter unit of claim 1 including an inductive element seriallyconnected to said lead at an end of said section, and said metallizedfilm extends around at least the perimeter of said element.

5. The filter unit of claim 1 wherein said film is heat shrinkabletubing which is thermally treated in situ to shrink tightly around saidsection.

6. The filter unit of claim 1 including a conductive terminalconductively affixed to said other electrode at said other end, saidterminal having a substantially centrally located aperture therein, saidlead extending through said aperture and spaced from the walls thereof,and said film encircles the perimeter of said terminal with saidmetallic deposit thereof in contact with said perimeter.

7. The filter unit of claim 6 including a second capacitance sectionconvolutely wound concentric with the first section, said second sectionhaving one electrode extended at said one end and its other electrodeextended at said other end and in connection to said terminal thereat,an inductive element disposed on said one end in serial connectionbetween said lead and said one electrode of said second section, and aterminal lead extending from said one electrode of said other section soas to provide a w-type filter.

8. The filter unit of claim 6 including an inductive element disposedwithin said aperture, and said element serially connected to said leadwithin said aperture to provide an L-type filter.

9. The filter unit of claim 8 including another inductive elementdisposed on said one end of said section and said other element inserial connection to said lead to provide a T-type filter.

1. A filter unit comprising a capacitive section having at least a pairof electrodes separated by dielectric material and convolutely wound incapacitive relation, one of said electrodes extended from one end ofsaid section and interconnected thereat, the other of said electrodesextended from the other end of said section and interconnected thereat;a lead extended through the center of said section, said lead inconnection to said one electrode at said one end and insulated from saidother electrode, and said other electrode vOlutely extended by ametallized film circumferentially shrunk around said section with itsmetallic deposit in connection to said other electrode at said other endfor providing a circumferential electrostatic shield of said unit. 2.The filter unit of claim 1 including an inductive element disposed atone end of said section in connection to said one electrode.
 3. Thefilter unit of claim 1 wherein said metallized film is a sleeve ofshrinkable material, said sleeve having said metallic deposit on theinner surface thereof, and said sleeve shrunk fit around said section toprovide said connection between said deposit and said other electrode.4. The filter unit of claim 1 including an inductive element seriallyconnected to said lead at an end of said section, and said metallizedfilm extends around at least the perimeter of said element.
 5. Thefilter unit of claim 1 wherein said film is heat shrinkable tubing whichis thermally treated in situ to shrink tightly around said section. 6.The filter unit of claim 1 including a conductive terminal conductivelyaffixed to said other electrode at said other end, said terminal havinga substantially centrally located aperture therein, said lead extendingthrough said aperture and spaced from the walls thereof, and said filmencircles the perimeter of said terminal with said metallic depositthereof in contact with said perimeter.
 7. The filter unit of claim 6including a second capacitance section convolutely wound concentric withthe first section, said second section having one electrode extended atsaid one end and its other electrode extended at said other end and inconnection to said terminal thereat, an inductive element disposed onsaid one end in serial connection between said lead and said oneelectrode of said second section, and a terminal lead extending fromsaid one electrode of said other section so as to provide a pi -typefilter.
 8. The filter unit of claim 6 including an inductive elementdisposed within said aperture, and said element serially connected tosaid lead within said aperture to provide an L-type filter.
 9. Thefilter unit of claim 8 including another inductive element disposed onsaid one end of said section and said other element in serial connectionto said lead to provide a T-type filter.